The only one that is of concern to me is the sybil attack vector but that is the hardest one (and most relevant to nearly all coins out there) to find a solution to. Evan is already introducing 3-party joins as a start, who knows if there will be a better solution (or even complimentary solution to what's there already) in the future. It would be interesting to see a rerun of attack vectors over 8 rounds with 3 party joins and see how things stack up in the near-term.